Polishing pad configuration and chemical mechanical polishing system

ABSTRACT

A polishing pad includes and upper portion and one or more lower portions. The upper portion has an upper surface for attachment to a pad carrier and a first lateral dimension. The one or more lower portions project downward from the upper portion. A bottom surface of the one or more lower portions provide a contact surface to contact a substrate during chemical mechanical polishing. Each lower portion has a second lateral dimension that is less than the first lateral dimension. A total surface area of the contact surface from the one or more lower portions is no more than 10% of a surface area of the upper surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of and claimspriority to U.S. application Ser. No. 14/334,608, filed on Jul. 17,2014, the entire disclosure of which is incorporated by reference.

TECHNICAL FIELD

This disclosure relates to the architecture of a chemical mechanicalpolishing (CMP) system.

BACKGROUND

An integrated circuit is typically formed on a substrate by thesequential deposition of conductive, semiconductive, or insulativelayers on a silicon wafer. One fabrication step involves depositing afiller layer over a non-planar surface and planarizing the filler layer.For certain applications, the filler layer is planarized until the topsurface of a patterned layer is exposed. A conductive filler layer, forexample, can be deposited on a patterned insulative layer to fill thetrenches or holes in the insulative layer. After planarization, theportions of the metallic layer remaining between the raised pattern ofthe insulative layer form vias, plugs, and lines that provide conductivepaths between thin film circuits on the substrate. For otherapplications, such as oxide polishing, the filler layer is planarizeduntil a predetermined thickness is left over the non-planar surface. Inaddition, planarization of the substrate surface is usually required forphotolithography.

Chemical mechanical polishing (CMP) is one accepted method ofplanarization. This planarization method typically requires that thesubstrate be mounted on a carrier or polishing head. The exposed surfaceof the substrate is typically placed against a rotating polishing pad.The carrier head provides a controllable load on the substrate to pushit against the polishing pad. An abrasive polishing slurry is typicallysupplied to the surface of the polishing pad.

SUMMARY

The present disclosure provides systems and apparatus for polishing ofsubstrates, e.g., “touch-up polishing,” in which polishing is performedon a limited area of the front surface of the substrate.

In one aspect, a chemical mechanical polishing system includes asubstrate support, a movable pad support and a drive system. Thesubstrate support is configured to hold a substrate in a substantiallyfixed angular orientation during a polishing operation. The movable padsupport is configured to hold a polishing pad having a diameter nogreater than a radius of the substrate. The drive system is configuredto move the pad support and polishing pad in an orbital motion while thepolishing pad is in contact with an upper surface of the substrate. Theorbital motion has a radius of orbit no greater than a diameter of thepolishing pad and maintains the polishing pad in a fixed angularorientation relative to the substrate.

In another aspect, a chemical mechanical polishing system includes asubstrate support, a polishing pad, a movable pad support and a drivesystem. The substrate support is configured to hold the substrate in asubstantially fixed angular orientation during a polishing operation.The polishing pad has a contact area for contacting the substrate, thecontact area having a diameter no greater than a radius of thesubstrate. The movable pad support is configured to hold the polishingpad. The drive system is configured to move the pad support andpolishing pad in an orbital motion while the contact area of thepolishing pad is in contact with an upper surface of the substrate. Theorbital motion has a radius of orbit no greater than a diameter of thepolishing pad and maintains the polishing pad in a fixed angularorientation relative to the substrate.

In another aspect, a method of chemical mechanical polishing includesbringing a polishing pad into contact with a substrate in a contact areahaving a diameter no greater than a radius of the substrate, andgenerating relative motion between the polishing pad and the substratewhile the contact area of the polishing pad is in contact with an uppersurface of the substrate. The relative motion includes an orbital motionhaving a radius of orbit no greater than a diameter of the polishingpad. The polishing pad is maintained in a substantially fixed angularorientation relative to the substrate during the orbital motion.

In another aspect, a chemical mechanical polishing system includes asubstrate support configured to hold a substrate during a polishingoperation, a polishing pad support; a polishing pad held by the padsupport, and a drive system configured to generate relative motionbetween the substrate support and the polishing pad support. Thepolishing pad has an upper portion secured to the polishing pad supportand a lower portion projecting downward from the upper portion. An uppersurface of the upper portion abuts the polishing pad support. A bottomsurface of the lower portion provides a contact surface to contact a topsurface of the substrate during polishing. The contact surface issmaller than the top surface of the substrate. The upper portion has afirst lateral dimension and the lower portion has a second lateraldimension that is less than the first lateral dimension; and

In another aspect, a polishing pad includes and upper portion and one ormore lower portions. The upper portion has an upper surface forattachment to a pad carrier and a first lateral dimension. The one ormore lower portions project downward from the upper portion. A bottomsurface of the one or more lower portions provide a contact surface tocontact a substrate during chemical mechanical polishing. Each lowerportion has a second lateral dimension that is less than the firstlateral dimension. A total surface area of the contact surface from theone or more lower portions is no more than 10% of a surface area of theupper surface.

In another aspect, a chemical mechanical polishing system includes asubstrate support configured to hold a substantially circular substrateduring a polishing operation, a polishing pad support, a polishing padheld by the pad support, and a drive system configured to generaterelative motion between the substrate support and the polishing padsupport. The polishing pad has an arc-shaped contact area, and a centerpoint of an arc defined by the arc-shaped contact area is substantiallyaligned with a center of the substrate held by the substrate support.

In another aspect, a polishing assembly includes a polishing pad supportand a polishing pad held by the pad support. The polishing pad supportincludes an annular member and a recess with a substrate-facing opening.The polishing pad has a polishing surface to contact a substrate duringpolishing. A perimeter portion of the polishing pad is vertically fixedto the annular member and a remainder of the polishing pad within theperimeter portion is vertically free. The substrate-facing opening ofthe polishing pad support is sealed by the polishing pad to define apressurizable chamber to provide an adjustable pressure on a backsurface of the polishing pad.

In another aspect, a polishing pad includes an upper portion, one ormore lower portions, and a plurality of apertures. The upper portion hasan upper surface for attachment to a pad carrier and a first lateraldimension. The one or more lower portions project downward from theupper portion. A bottom surface of the one or more lower portionsprovide a contact surface to contact a substrate during chemicalmechanical polishing. Each lower portion has a second lateral dimensionthat is less than the first lateral dimension such that the upperportion projects past all lateral sides of the lower portion. Theplurality of apertures are in the upper surface of the upper portion toreceive projections from the pad carrier. The apertures are positionedin a section of the upper portion of the polishing pad laterally outwardof the lower portion.

Advantages of the invention may include one or more of the following.

A small pad that undergoes an orbiting motion can be used to compensatefor non-concentric polishing uniformity. The orbital motion can providean acceptable polishing rate while avoiding overlap of the pad withregions that are not desired to be polished, thus improving substrateuniformity. In addition, in contrast with rotation, an orbital motionthat maintains a fixed orientation of the polishing pad relative to thesubstrate can provide a more uniform polishing rate across the regionbeing polished.

Making the top portion of the polishing pad that is secured to thepolishing pad support laterally wider than the bottom protrusion thatmakes contact with the substrate can increase the available area forconnection of the pad to the support, e.g., by a pressure sensitiveadhesive. This can make the polishing pad less susceptible todelamination during the polishing operation.

A polishing pad with an arc-shaped contact area for contacting thesubstrate can provide improved polishing rate, while maintainingsatisfactory radial resolution of the polishing region.

An alignment feature can ensure that the limited contact area of thepolishing pad is placed in a known position laterally relative to thepad support, thus reducing the likelihood of polishing an undesiredregion of the substrate.

Providing a portion of the polishing pad that flexes can reducingflexing of the portion of the contact surface of the polishing pad, thusimproving the likelihood that the region polished matches what isexpected by the operator.

Grooves in the projection of the polishing pad can facilitate transportof slurry, and can thus improve the polishing rate.

A portion of the polishing pad that does not contact the substrate canbe formed out of lower-cost material, thus reducing the total pad cost.

A pad carrier that permits control of size of the portion of the contactarea that is loaded against the substrate permits the loading area to bematched to the size of the spot to be polished, thus improvingthroughput while avoiding polishing an undesired region of thesubstrate.

Overall, non-uniform polishing of the substrate can be reduced, and theresulting flatness and finish of the substrate can be improved.

Other aspects, features, and advantages of the invention will beapparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional side view of a polishing system;

FIG. 2 is a schematic cross-sectional side view of an implementation ofa polishing system that includes a vacuum chuck to hold the substrate;

FIG. 3 is a schematic cross-sectional side view of an implementation ofa polishing system with a polishing pad that does not include a downwardprojection;

FIG. 4 is a schematic cross-sectional side view of an implementation ofa polishing system with a polishing pad that has an upper layer that hasa larger diameter than the substrate, and a downward projection with asmaller diameter than the substrate;

FIG. 5 is a schematic cross sectional top view illustrating a polishingpad that moves in an orbit while maintaining a fixed angularorientation;

FIG. 6 is a schematic cross-sectional top view of the polishing padsupport and drive train system of a polishing system;

FIG. 6A is a schematic cross-sectional top view of the system of FIG. 6with relation to a substrate;

FIG. 6B is a schematic cross-sectional top view of the system of FIG. 6,with a quarter revolution turn with respect to FIG. 6A;

FIG. 7A is a schematic cross-sectional side view of a movable polishingpad support connected to the polishing pad with a plurality of clamps;

FIG. 7B is a schematic cross-sectional view of an implementation of amovable polishing pad support that includes an interior pressurizedspace enclosed by an internal membrane;

FIG. 8A is a schematic cross-sectional side view of the movablepolishing pad support of FIG. 7B in a state of low pressure;

FIG. 8B is a schematic cross-sectional side view of the movablepolishing pad support of FIG. 7B in a state of high pressure;

FIG. 9 is a schematic bottom view of a contact area of a polishing pad;

FIGS. 10A and 10B are schematic cross-sectional side views ofimplementations of a polishing pad;

FIG. 11 is a schematic cross-sectional side view of anotherimplementation of a movable polishing pad support;

FIG. 12 is a schematic top view of an implementation of a polishingsystem with a polishing pad that has an arc-shaped projection layerwhich forms a corresponding arc-shaped loading area; and

FIG. 13 is a schematic cross-sectional side view of an implementation ofa polishing system with an arc-shaped polishing surface that undergoesorbital motion.

FIG. 14 is a schematic top view of a polishing pad.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

1. Introduction

Some polishing processes result in thickness non-uniformity across thesurface of the substrate. For example, a bulk polishing process canresult in under-polished regions on the substrate. To address thisproblem, after the bulk polishing it is possible to perform a “touch-up”polishing process that focuses on portions of the substrate that wereunderpolished.

In a bulk polishing process, polishing occurs over all of the frontsurface of the substrate, albeit potentially at different rates indifferent regions of the front surface. Not all of the surface of thesubstrate might be undergoing polishing at a given instant in a bulkpolishing process. For example, due to the presence of grooves in thepolishing pad, some portion of the substrate surface might not be incontact with the polishing pad. Nevertheless, over the course of thebulk polishing process, due to the relative motion between the polishingpad and substrate, this portion is not localized, so that all of thefront surface of the substrate is subjected to some amount of polishing.

In contrast, in a “touch-up” polishing process, the polishing pad cancontact less than all of the front surface of the substrate. Inaddition, the range of motion of the polishing pad relative to thesubstrate is configured such that over the course of the touch-uppolishing process, the polishing pad contacts only a localized region ofthe substrate, and a significant portion (e.g., at least 50%, at least75%, or at least 90%) of the front surface of the substrate nevercontacts the polishing pad and thus is not subject polishing.

As noted above, some bulk polishing processes result in non-uniformpolishing. In particular, some bulk polishing processes result inlocalized non-concentric and non-uniform spots that are underpolished.In a touch-up polishing process, a polishing pad that rotates about acenter of the substrate may be able to compensate for concentric ringsof non-uniformity, but may not be able to address localizednon-concentric and non-uniform spots, e.g., angular asymmetry in thethickness profile. However, a small pad, e.g., a small pad thatundergoes an orbiting motion, can be used to compensate fornon-concentric polishing uniformity.

Referring to FIG. 1, a polishing apparatus 100 for polishing localizedregions of the substrate includes a substrate support 105 to hold asubstrate 10, and a movable polishing pad support 300 to hold apolishing pad 200. The polishing pad 200 includes a polishing surface250 that has a smaller diameter than the radius of the substrate 10being polished.

The polishing pad support 300 is suspended from a polishing drive system500 which will provide motion of the polishing pad support 300 relativeto the substrate 10 during a polishing operation. The polishing drivesystem 500 can be suspended from a support structure 550.

In some implementations, a positioning drive system 560 is connected tothe substrate support 105 and/or the polishing pad support 300. Forexample, the polishing drive system 500 can provide the connectionbetween the positioning drive system 560 and the polishing pad support300. The positioning drive system 560 is operable to position the padsupport 300 at a desired lateral position above the substrate support105. For example, the support structure 550 can include two linearactuators 562 and 564, which are oriented perpendicular relative to oneanother over the substrate support 105, to provide the positioning drivesystem 560. Alternatively, the substrate support 105 could be supportedby two linear actuators. Alternatively, the substrate support 105 can berotatable, and the polishing pad support 300 can be suspended from asingle linear actuator that provides motion along a radial direction.Alternatively, the polishing pad support can be suspended from a rotaryactuator 508 and the substrate support 105 can be rotatable with arotary actuator 506.

Optionally, a vertical actuator 506 and/or 508 can be connected to thesubstrate support 105 and/or the polishing pad support 300. For example,the substrate support 105 can be connected to a vertically drivablepiston 506 that can lift or lower the substrate support 105.

The polishing apparatus 100 includes a port 60 to dispense polishingliquid 65, such as abrasive slurry, onto the surface 12 of the substrate10 to be polished. The polishing apparatus 100 can also include apolishing pad conditioner to abrade the polishing pad 200 to maintainthe polishing pad 200 in a consistent abrasive state.

In operation, the substrate 10 is loaded onto the substrate support 105,e.g., by a robot. The positioning drive system 500 positions thepolishing pad support 300 and polishing pad 200 at a desired position onthe substrate 10, and the vertical actuator 506 moves the substrate 10into contact with the polishing pad 200 (or vice versa with actuator508). The polishing drive system 500 generates the relative motionbetween the polishing pad support 300 and the substrate support 105 tocause polishing of the substrate 10.

During the polishing operation, the positioning drive system 560 canhold the polishing drive system 500 and substrate 10 substantially fixedrelative to each other. For example, the positioning system can hold thepolishing drive system 500 stationary relative to the substrate 10, orcan sweep the polishing drive system 500 slowly (compared to the motionprovided to the substrate 10 by the polishing drive system 500) acrossthe region to be polished. For example, the instantaneous velocityprovided to the substrate by the positioning drive system 500 can beless than 5%, e.g., less than 2%, of the instantaneous velocity providedto the substrate by the polishing drive system 500.

The polishing system also includes a controller 90, e.g., a programmablecomputer. The controller can include a central processing unit 91,memory 92, and support circuits 93. The controller's 90 centralprocessing unit 91 executes instructions loaded from memory 92 via thesupport circuits 93 to allow the controller to receive input based onthe environment and desired polishing parameters and to control thevarious actuators and drive systems.

For a “touch-up” polishing operation, the controller 90 is programmed tocontrol the positioning drive system 560 such even if the polishingdrive system 500 is being swept slowly, the range of motion of thepolishing drive system 500 is constrained so that over the course of thetouch-up polishing process, a significant portion (e.g., at least 50%,at least 75%, or at least 90%) of the front surface of the substratenever contacts the polishing pad and thus is not subject polishing.

2. The Polishing System

A. The Substrate Support

Referring to FIG. 1, the substrate support 105 is plate-shaped bodysituated beneath the polishing pad support. The upper surface 116 of thebody provides a loading area large enough to accommodate a substrate tobe processed. For example, the substrate can be a 200 to 450 mm diametersubstrate. The upper surface 116 of the substrate support 105 contactsthe back surface of the substrate 10 (i.e., the surface that is notbeing polished) and maintains its position.

The substrate support 105 is about the same radius as the substrate 10,or larger. In some implementations, the substrate support 105 isslightly narrower (e.g., see FIG. 2) than the substrate, e.g., by 1-2%of the substrate diameter. When placed on the support 105, the edge ofthe substrate 10 slightly overhangs the edge of the support 105. Thiscan provide clearance for an edge grip robot to place the substrate onthe support. In some implementations, the substrate support 105 is widerthan the substrate. In this case, a robot with an end effector having avacuum chuck can be used to place the substrate on the support. Ineither case, the substrate support 105 can make contact with a majorityof the surface the backside of the substrate.

In some implementations, as shown in FIG. 1, the substrate support 105maintains the substrate 10 position during polishing operation with aclamp assembly 111. In some implementations, the clamp assembly 111 canbe a single annular clamp ring 112 that contacts the rim of the topsurface of the substrate 10. Alternatively, the clamp assembly 111 caninclude two arc-shaped clamps 112 that contact the rim of the topsurface on opposite sides of the substrate 10. The clamps 112 of theclamp assembly 111 can be lowered into contact with the rim of thesubstrate by one or more actuators 113. The downward force of the clamprestrains the substrate from moving laterally during polishingoperation. In some implementations, the clamp(s) include downwardly aprojecting flange 114 that surrounds the outer edge of the substrate.

In some implementations, as shown in FIG. 2, the substrate support 105is a vacuum chuck 106. The vacuum chuck 106 includes a chamber 122 and aplurality of ports 124 connecting the chamber 122 to the surface 116that supports the substrate 10. In operation, air can be evacuated fromof the chamber 122, e.g., by a pump 129, thus applying suction throughthe ports 124 to hold the substrate in position on the substrate support106.

In some implementations, as shown in FIG. 3, the substrate support 105includes a retainer 131. The retainer 131 can be attached to and projectabove the surface 116 that supports the substrate 10. Typically theretainer is at least as thick (measured perpendicular to the surface 12)as the substrate 10. In operation, the retainer 131 surrounds thesubstrate 10. For example, the retainer 131 can be an annular body witha diameter slightly larger than the diameter of the substrate 10. Duringpolishing, friction from the polishing pad 200 can generate a lateralforce on the substrate 10. However, the retainer 131 constrains thelateral motion of the substrate 10.

The various substrates support features described above can beoptionally be combined with each other. For example, the substratesupport can include both a vacuum chuck and a retainer.

In addition, although substrate support configurations are shown inconjunction with the pressure sensitive adhesive movable pad supportconfigurations for ease of illustration, they can be used with any ofthe embodiments of the pad support head and/or drive system describedbelow.

B. The Polishing Pad

Referring to FIG. 1, the polishing pad 200 has a polishing surface 250that is brought into contact with the substrate 10 in a contact area,also called a loading area, during polishing. The polishing surface 250can be of a smaller diameter than the radius of the substrate 10. Forexample, for the diameter of the polishing surface can be about can beabout 5-10% of the diameter of the substrate. For example, for waferthat ranges from 200 mm to 300 mm in diameter, the polishing surface canbe between 10 and 30 mm in diameter. A smaller polishing surfaceprovides more precision but lower throughput.

In some implementations, less than 1% of the substrate surface can becontacted at any given time by the polishing surface. In general, whilethis can be useful for a touch-up polishing operation, such a small areawould not be acceptable for a bulk polishing operation due to lowthroughput.

In some implementations, e.g., as shown in FIG. 3, the entire polishingpad, e.g., as measured to the outer edge of the pad, has a smallerdiameter than the radius of the substrate 10. For example, for thediameter of the polishing pad can be about can be about 5-10% of thediameter of the substrate.

In the example in FIG. 1, the polishing pad 200 is located above theupper surface of the substrate 10, and includes an upper portion 270which is coupled to the bottom of the movable pad support 300, and alower portion 260 which has a bottom surface 250 that makes contact withthe substrate 10 during polishing operation. In some instances, as shownin FIG. 1, the bottom portion 260 of the polishing pad 200 is providedby a protrusion from a wider upper portion 270. The bottom surface 250of the protrusion 260 comes into contact with the substrate duringpolishing operation and provides the polishing surface.

In the example in FIG. 1, the movable pad support 300 is coupled to thetop portion 270 of the polishing pad 200 using a pressure sensitiveadhesive 231. The pressure sensitive adhesive 231, applied between thebottom surface of the polishing pad support 300 and the top surface 270of the polishing pad, maintains the polishing pad 200 on the pad support300 coupling during the polishing operation.

By making the upper portion 270 of the polishing pad 200 wider than thelower portion 260, the available surface area for the adhesive 231 isincreased. Increasing the surface area of the adhesive 231 can improvethe bond strength between the pad 200 and pad support, and reduce therisk of delamination of the polishing pad during polishing.

Referring to FIG. 3, the polishing pad 203 can have the same radius inits bottom portion 260 as in its top portion 273. However, when apressure sensitive adhesive 231 provides the coupling between the padand the movable pad support 300, it is preferable for the bottom portion263 to be narrower than the top portion 273.

Referring to FIG. 5, the contact area 5 of the polishing pad can be adisk-shaped geometry 5 formed by a disk-shaped bottom protrusion of thepolishing pad.

Referring to FIGS. 9A and 9B, the contact area 901 of the polishing pad110 which makes contact with the substrate 10 can be an arc-shapedcontact area 901 formed by an arc-shaped protrusion 290 of the polishingpad.

Referring to FIG. 1, in some implementations the diameter of the upperportion 270 of the polishing pad 200 can be smaller than the diameter ofthe substrate 10.

Referring to FIG. 4, in some implementations the diameter of the upperportion 274 of the polishing pad 204 can be larger than the diameter ofthe substrate 10.

Referring to FIG. 1, the polishing pad 200 can consist of a single layerof uniform composition. In this case, the material composition of theupper portion 270 and of the lower portion 260, also called theprotrusion 260, are the same.

Referring to FIG. 10B, in some implementations, the polishing pad 200can include two or more layers of different composition, e.g., apolishing layer 1062 and a more compressible backing layer 1052.Optionally, an intermediate pressure sensitive adhesive layer 1032 canbe used to secure the polishing layer 1061 to the backing layer 1061. Inthis case, the upper portion 1221 can correspond to the backing layer102 and the lower portion 1222 can correspond to the polishing layer1062. The polishing pad can be coupled to a polishing pad support viathe pressure sensitive adhesive layer 231.

Referring to FIG. 10A, in some implementations, the polishing pad caninclude two or more layers of different composition, and the upperportion 1221 of the polishing pad 200 can include both the backing layer1052 and an upper section 1064 of the polishing layer 1062. Thus, thepolishing layer 1062 includes both a lower section 1066 that providesthe protrusion 1222 and the upper section 1062, with the supper section1064 wider than the lower section 1066.

The polishing pad can be coupled to a polishing pad support via thepressure sensitive adhesive layer 321.

In either implementation shown in FIG. 10A or FIG. 10B, the polishinglayer 1062 can consist of a single layer of uniform composition. Forexample, in either implementation shown in FIG. 10A or FIG. 10B, theportion of the pad that contacts the substrate can be of a conventionalmaterial, e.g., a microporous polymer such as polyurethane.

Referring to FIG. 10A, the backing layer 1052 can be relatively soft toallow for better polishing pad flexibility when polishing an unevensubstrate surface spot. The polishing layer 1064 can be a hardpolyurethane.

Referring to FIG. 10B, the backing layer 1052 can be relatively soft,but also can be a flexible incompressible layer made of material, suchas polyethylene terephthalate, e.g., Mylar™. For example, such a padconfiguration can be used in implementation in which the polishing padof FIG. 10B is coupled to the pressurized chamber polishing pad supportof FIG. 11. The polishing layer 1062 can be a hard polyurethane.

Referring to FIG. 11, in some implementations, the polishing pad 205 caninclude an upper portion 275 and a lower portion 260. The polishing pad205 has a thicker lateral section 267 which includes the combined lowerportion 260 and upper portion 275. The upper portion 275 extendslaterally 285 on either side of the thicker section 267. The lateralside sections 285 flex in response to pressure on the thicker section267. The thicker section 267 can have a pad thickness of about 2 mm inthe polishing area, which is similar to a large sized pad. The padthickness in the flexing lateral sections 285 can be about 0.5 mm.

In some implementations, the bottom surface of the lower portion of thepolishing pad 200 can include grooves to permit transport of slurryduring a polishing operation. The grooves 299 can be shallower than thedepth of the lower portion 260 (e.g., see FIG. 11). However, in someimplementations the lower portion does not include grooves. If thepolishing pad includes grooves, the grooves 299 can extend entirelyacross the lateral width of the lower portion 260. In addition, thegrooves can be shallower than the vertical thickness of the lowerportion 260, i.e., the grooves pass vertically partially but notentirely through the lower portion 260.

Referring to FIG. 9, the bottom surface 1900 of the polishing pad 200can be an arc-shaped area. If such a polishing pad includes grooves, thegrooves 299 can extend entirely across the lateral width of thearc-shaped area. The grooves 299 can be spaced at uniform pitch alongthe length of the arc-shaped area. Each grooves 299 can extend along aradius that passes through the groove and the center 1903 of thearc-shaped area, or be positioned at an angle, e.g., 45°, relative tothe radius.

Referring to FIG. 14, in some implementations, the polishing pad 200includes alignment features that mate with matching features on the padsupport 300 to ensure that the polishing pad 200, and the lower portion260 that provides the contact area 250, is in a known lateral positionrelative to the pad support 300.

For example, the polishing pad 200 can include recesses 1402 formed inthe back surface of the polishing pad 200. The recesses 1402 can bemachine drilled into the polishing pad in a known position relative tothe contact area 250. The recesses 1402 can be positioned in the thinflange or outer lateral portion 285 of the upper portion 270 of thepolishing pad 200. The recesses can extend partially or entirely throughthe polishing pad. The pad support 300 can include pins 1404, e.g.,projecting downwardly from the plate, that fit into the recesses 1402.

As another example, at least some the edges 1406 of the polishing pad200 can be machined after the contact area 250 is defined on thepolishing pad 200. The pad support 300 can include a recess machinedinto the support plate. The edges of the recess include alignmentsurfaces, and the edges of the 1406 of the polishing pad are positionedto abut the alignment surface of the recess in the plate.

The lower portion 260 of the polishing pad 200 that contacts thesubstrate can be formed of a high-quality material, e.g., a materialmeeting high precision specifications of rigidity, porosity, and thelike. However, other portions of the polishing pad that do not contactthe substrate need not meet such high precision specifications, andtherefore can be formed out of lower-cost material. This can reduce thetotal pad cost.

C. The Drive System and Orbital Motion of the Pad

Referring to FIGS. 1 and 5, the polishing drive system 500 can beconfigured to move the coupled polishing pad support 300 and polishingpad 200 in an orbital motion above the substrate 10 during the polishingoperation. In particular, as shown in FIG. 5, the polishing drive system500 can be configured to maintain the polishing pad in a fixed angularorientation relative to the substrate during the polishing operation.

Referring to FIG. 5, the radius of orbit 20 of the polishing pad incontact with the substrate is preferably smaller than the diameter 22 ofthe contact area. For example, the radius of orbital can be about 5-50%,e.g., 5-20%, of the diameter of the contact area. For a 20 to 30 mmdiameter contact area, the radius of orbit can be 1-6 mm. This achievesa more uniform velocity profile in the loading area 5. The polishing padcan revolve in its orbit at a rate of 1,000 to 5,000 revolutions perminute (“rpm”).

Referring to FIG. 6, the drive train can include a mechanical systembase 910 which achieves orbital motion with a single actuator 915. Amotor output shaft 924 is connectively coupled to a cam 922. The cam 922extends into a recess 928 in the polishing pad holder 920. During thepolishing operation, the motor output shaft 924 rotates around arotational axis 990, causing the cam 922 to revolve the polishing padholder 920. A plurality of anti-rotation links 912 extend from themechanical system base 910 to the upper portion of the polishing padholder 920 to prevent rotation of the pad holder 920. The anti-rotationlinks 912, in conjunction with motion of cam 922, achieve orbital motionof the polishing pad support, in which the angular orientation of thepolishing pad holder 920 does not change during polishing operation.

Orbital motion, as depicted in FIGS. 6A and 6B, can maintain a fixedangular orientation of the polishing pad relative to the substrateduring polishing operation. As the central motor output shaft 620rotates, the cam 625, in combination with anti-rotational links 630connecting the mechanical system base above to the polishing padsupport, translates the rotational motion into orbital motion for thepolishing pad 610. This achieves a more uniform velocity profile thansimple rotation.

In some implementations, the polishing drive system and the positioningdrive system are provided by the same components. For example, a singledrive system can include two linear actuators configured to move the padsupport head in two perpendicular directions. For positioning, thecontroller can cause the actuators to move the pad support to thedesired position on the substrate. For polishing, the controller cancause the actuators to the actuators to move the pad support in theorbital motion, e.g., by applying phase offset sinusoidal signals to thetwo actuators.

Referring to FIG. 1, in some implementations, the polishing drive system500 can include two rotary actuators. For example, the polishing padsupport can be suspended from a rotary actuator 508, which in turn issuspended from a second rotary actuator 509. During the polishingoperation, the second rotary actuator 509 rotates an arm 510 that sweepsthe polishing pad support 300 in the orbital motion. The first rotaryactuator 508 rotates, e.g., in the opposite direction but at the samerotation rate as the second rotary actuator 509, to cancel out therotational motion such that the polishing pad assembly orbits whileremaining in a substantially fixed angular position relative to thesubstrate.

D. Pad Support

The movable pad support 300 holds the polishing pad, and is coupled tothe polishing drive system 500.

In some implementations, e.g., as shown in FIGS. 1-4, the pad support300 is a simple rigid plate. The lower surface 311 of the plate issufficiently large to accommodate the upper portion 270 of the polishingpad 200.

However, the pad support 300 can also include an actuator 508 to controla downward pressure of the polishing pad 200 on the substrate 10.

In the example in FIG. 7A, a pad support 300 that can apply anadjustable pressure on the polishing pad 200 is shown. The pad support300 includes a base 317 that is coupled to the polishing drive system500. A bottom of the base 317 includes a recess 327. The pad support 300includes a clamp 410 that hold the rim of the polishing pad 200 on thebase 317. The polishing pad 200 can cover the recess 327 to define apressurizable chamber 426. By pumping a fluid into or out of the chamber426, downward pressure of the polishing pad 200 on the substrate 10 canbe adjusted.

In the some implementations, as in FIGS. 7B, 8A, and 8B the pad support300 can have an interior membrane 405 defining a first pressurizablechamber 406 between the membrane 405 and the base 317. The membrane ispositioned to contact the side 275 of the polishing pad 200 farther fromthe polishing surface 258. The membrane 405 and the chamber 406 areconfigured such that when the pad support 300 holds the polishing pad200 during a polishing operation, the pressure in the chamber 406controls the size of the loading area 809 of the polishing pad 200 onthe substrate 10. When the pressure inside the chamber increases, themembrane expands its radius, applying pressure to a larger portion ofthe bottom protrusion layer of the pad and thus increasing the area ofthe loading area 810. When pressure decreases, the result is asmaller-sized loading area 809.

Referring to FIG. 11, in some implementations, the polishing pad support315 can include an internal pressurizable chamber 325 formed by walls320 of the polishing pad support 315. The chamber 325 can have asubstrate-facing opening 327. The opening 327 can be sealed by securingthe polishing pad 200 to the polishing pad support 315, e.g., by a clamp410. The pressure in the pressure chamber 425 can be dynamicallycontrolled, e.g., by a controller and hydrostatic pump, during apolishing operation to adjust to the non-uniform spot being polished.

Referring to FIG. 12, in some implementations, the contact area 1301 ofthe polishing pad 20 can be arc-shaped area. For example, the protrusioncan be arc-shaped. The drive system 500 can rotate the arc around acenter 1302 of the substrate 10.

Referring to FIG. 13, in some embodiments, the polishing pad 200 contactarea 901 can be an arc-shaped area that undergoes orbital motionrelative to the substrate 10.

3. Conclusion

The size of a spot of non-uniformity on the substrate will dictate theideal size of the contact area during polishing of that spot. If thecontact area is too large, correction of underpolishing of some areas onthe substrate can result in overpolishing of other areas. On the otherhand, if the contact area is too small, the pad will need to be movedacross the substrate to cover the underpolished area, thus decreasingthroughput.

In a substrate processing operation, the substrate can first besubjected to a bulk polishing process in which polishing is performedover the entirety of the front surface of the substrate. Optionally,after the bulk polishing operation, non-uniformity of the substrate canbe measured, e.g., at an in-line or stand-alone metrology station. Thesubstrate can then be transported to the polishing apparatus 100 andsubjected to a touch-up polishing process. Control of the region to bepolished at the polishing apparatus can be based on identification ofunder-polished regions of the substrate from either historical data,e.g., thickness measurements made during qualification, or frommeasurements of the substrate at the in-line or stand-alone metrologystation.

The entire polishing system could be arranged with the front surface ofthe substrate positioned vertically or facing downwardly (relative togravity). However, an advantage of having the front surface of thesubstrate be facing upwardly is that this permits slurry to bedistributed on the face of the substrate. Due to the larger size of thesubstrate relative to the polishing surface of the polishing pad, thiscan improve slurry retention and thus reduce slurry usage.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, the substrate support could, in some embodiments, include itsown actuators capable of moving the substrate into position relative tothe polishing pad. As another example, although the system describedabove includes a drive system that moves the polishing pad in theorbital path while the substrate is held in a substantially fixedposition, instead the polishing pad could be held in a substantiallyfixed position and the substrate moved in the orbital path. In thissituation, the polishing drive system could be similar, but coupled tothe substrate support rather than the polishing pad support. Althoughgenerally circular substrate is assumed, this is not required and thesupport and/or polishing pad could be other shapes such as rectangular(in this case, discussion of “radius” or “diameter” would generallyapply to a lateral dimension along a major axis).

Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. A chemical mechanical polishing system,comprising: a substrate support configured to hold a substrate during apolishing operation; a polishing pad support; a polishing pad held bythe pad support, the polishing pad having an upper portion secured tothe polishing pad support and a lower portion projecting downward fromthe upper portion, wherein an upper surface of the upper portion abutsthe polishing pad support, a bottom surface of the lower portionprovides a contact surface to contact a top surface of the substrateduring polishing, the contact surface being smaller than the top surfaceof the substrate, and the upper portion has a first lateral dimensionand the lower portion has a second lateral dimension that is less thanthe first lateral dimension; and a drive system configured to generaterelative motion between the substrate support and the polishing padsupport.
 2. The chemical mechanical polishing system of claim 1, whereinthe polishing pad support comprises a plate having a surface that spansthe polishing pad, and substantially all of an upper surface of theupper portion of the polishing pad abuts the surface of the plate. 3.The chemical mechanical polishing system of claim 2, further comprisingan adhesive holding the polishing pad on the pad support.
 4. Thechemical mechanical polishing system of claim 1, wherein the polishingpad support comprises an annular member, a perimeter portion of an uppersurface of the upper portion of the polishing pad abuts the annularmember, and a remainder of the upper surface within the perimeterportion does not contact the polishing pad support.
 5. The chemicalmechanical polishing system of claim 4, further comprising one or moreclamps holding a perimeter section of the polishing pad on the padsupport.
 6. The chemical mechanical polishing system of claim 4, whereinthe upper portion of the polishing pad includes a flexing section havinga greater flexibility than a section of the polishing pad above thecontact surface.
 7. The chemical mechanical polishing system of claim 6,wherein the upper portion of the polishing pad comprises a polyethyleneterephthalate sheet.
 8. The chemical mechanical polishing system ofclaim 1, further comprising a plurality of grooves for slurry transporton the contact surface of the lower portion of the polishing pad.
 9. Thechemical mechanical polishing system of claim 7, wherein the pluralityof grooves have a depth less than a thickness of the lower portion. 10.The chemical mechanical polishing system of claim 7, wherein at leastsome of the plurality of groove extend entirely across the lower portionof the polishing pad.
 11. The chemical mechanical polishing system ofclaim 1, further comprising a pressure chamber formed by an interiorchamber of the polishing pad support, the chamber having asubstrate-facing opening, and the opening being sealed by a coupling ofthe polishing pad to the polishing pad support.
 12. The chemicalmechanical polishing system of claim 1, comprising a plurality ofapertures in the upper surface of the polishing pad, and a plurality ofprojections from the polishing pad support that fit into the pluralityof apertures to align the lower portion relative to the polishing padsupport.
 13. A polishing pad, comprising: an upper portion having anupper surface for attachment to a pad carrier, the upper portion havinga first lateral dimension; and one or more lower portions projectingdownward from the upper portion, a bottom surface of the one or morelower portions providing a contact surface to contact a substrate duringchemical mechanical polishing, each lower portion having a secondlateral dimension that is less than the first lateral dimension, andwherein a total surface area of the contact surface from the one or morelower portions is no more than 10% of a surface area of the uppersurface.
 14. The polishing pad of claim 13, wherein at least the lowerportion is a polymer body of substantially uniform composition andhaving a plurality of pores distributed therein.
 15. The polishing padof claim 13, comprising a polishing layer, wherein the lower portionprojecting downward is formed in the polishing layer.
 16. The polishingpad of claim 13, wherein the pad includes a backing layer that is softerthan the polishing layer
 17. The polishing pad of claim 13, furthercomprising grooving for slurry transport on the bottom surface of theone or more lower portions.
 18. The polishing pad of claim 13, whereinthe one or more lower portion consist of a single projection
 19. Thepolishing pad of claim 13, wherein the polishing layer includes aflexible lateral section that is thinner than the lateral section whichmakes up the polishing area.
 20. The polishing pad of claim 13, whereinthe lower portion is a microporous polyurethane.